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  1. Male differentiation in humans is determined by the testis-determining gene, SRY, which is located on the short arm of the Y chromosome adjacent to the pseudoautosomal region.

  2. Cytogenetic studies of infertile males have revealed rare individuals with an apparently normal 46,XX karyotype. The majority of these sex-reversed XX males have inherited a small fragment of the Y chromosome, which includes SRY, transferred to the short arm of one of their X chromosomes.

  3. SRY mutations are found in 15 percent of XY females with pure gonadal dysgenesis.

  4. SRY induces the differentiation of Sertoli cells in the developing gonad. Sertoli cells produce anti-Mullerian hormone, which causes regression of the female internal genitalia; they also induce Leydig cells to secrete the androgens necessary for the development of male internal and external genitalia. Any genetic or environmental factor that prevents testis differentiation in 46,XY embryos leads to the development of a sex-reversed XY female.

  5. This chapter reviews the role of SRY in primary sex-reversal syndromes.

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